1. Field of the Invention
The present invention relates to an AC generator stator core to be mounted on a vehicle and a method for producing the AC generator stator core.
2. Description of the Prior Art
FIG. 13 is a sectional view of a conventional AC generator for a vehicle. This AC generator comprises a casing 3 consisting of a front bracket 1 and a rear bracket 2 which are connected together by a bolt 3B, a shaft 5 securing at one end thereof a pulley 4 which receives a turning force transmitted from an engine through a belt, a rotor 6 of Lundell type secured to the shaft 5, fans 6F secured to both sides of the rotor, a stator 7A secured to the inner wall surface within the casing 3, a slip ring 8 secured to the other end of the shaft 5 to supply the rotor 6 with an electric current, a pair of brushes 9 and 9 sliding on the slip ring 8, a brush holder 10 housing the brushes 9 and 9, a rectifier 11 electrically connected to the stator 7A to rectify an alternating current generated at the stator 7A to a direct current, a heat sink 12 attached to the brush holder 10, and a regulator 13 adhering to the heat sink 12 to regulate the size of the AC voltage generated at the stator 7A. Reference numerals 14a and 14b are bearings and numeral 15 is a bracket for attaching the AC generator to an engine.
Said rotor 6 is provided with a rotor coil 6A generating magnetic flux from the flow of an electric current, and a field core 6B arranged to cover a rotor coil 6A and forming magnetic pole therein by the magnetic flux of the rotor coil 6A. The field core 6B consists of a pair of mutually engaged field core bodies 6x and 6y. The field core bodies 6x and 6y are made of steel, each having a claw-shaped magnetic pole 62.
Said stator 7A is provided with a stator core 17A, and a stator coil 17B composed of conductor wires wound around the stator core 17A. The stator coil 17B generates an alternating current by the change of the magnetic flux from the rotor coil 6A in accordance with the rotation of the rotor 6.
In the above-mentioned AC generator for a vehicle, an electric current is supplied to the rotor coil 6A through the brushes 9 and 9 and the slip ring 8 from a battery (not shown) to generate magnetic flux, while the pulley 4 is driven by the engine to rotate the shaft 5 and the rotor 6, wherein the stator coil 17B is given a rotating magnetic field to cause an electromotive force therein. This electromotive force is rectified through diodes 16, 16 of the rectifier 11 to a direct current and the regulator 13 then regulates the size of the direct current to be charged to a battery.
FIG. 14 is a sectional view of a conventional brushless AC generator for a vehicle. In FIG. 14, the reference numerals shown represent the same or corresponding elements shown in FIG. 13 therefore their descriptions will be omitted. In this brushless AC generator for the vehicle, when the engine is started, an exciting current from the battery is supplied through the regulator 13A to an exciting coil housed in an exciting core 19 and the rotation of the shaft 5 allows the field core bodies 6x and 6y of the rotor 6 to rotate to generate the electromotive force at the stator coil 17B of the stator 7A. This AC electromotive force is rectified through the diodes 16 and 16 of the rectifier 11 to the direct current and the current size is then regulated by the regulator 13A and charged to the battery.
FIG. 15 is a simplified perspective view showing one example of a stator core 17A which is used in a conventional vehicle AC generator as shown in FIGS. 13 and 14. As shown in FIG. 16, the stator core 17A is formed to have a circular cylinder body by spirally laminating a long, thin metal sheet 17a (made of steel) which is formed by stamping and then several places on the outer periphery of the circular cylinder body is welded to be extended in the laminating direction. Thus, the stator core 17A is completed to have a predetermined thickness S in the laminating direction. The thin metal sheet 17a is provided with a recess 17b forming a slot 20 after lamination and a recess 17c forming a bolt clearance groove 21. FIG. 17 is a schematic plan view of the stator core 17A.
In FIG. 15, there is shown one example in which four welding places are provided, on the outer periphery, at intervals of about 90xc2x0 relative to a center of the circular cylinder body. Generally, there are provided four welding places from a core assembly strength point of view. Also, in case of welding., it is advisable to pick up the circular cylinder body first, by for example a chuck and the like to make each of the thin metal sheets 17a come closely into contact, and then weld the outer periphery of the circular cylinder body linearly from the top to bottom by using a jig that moves in a laminating direction of the circular cylinder body.
FIG. 15 shows the stator core 17A provided with slots 20. Each slot is wound by a one-phase coil, two-phase coil and three-phase coil, respectively to cause three-phase AC. FIG. 18 shows a completed stator core 7A. Each coil corresponding to one-phase is wound at intervals of two slots. Also, a conductor wire 17e forming the coil is secured within each slot 20 by varnish 22 as shown in FIG. 19 and the opening side of the slot 20 is also sealed by resin 23.
As shown in FIG. 16, the long, thin metal sheets 17a made by stamping are spirally laminated to provide a plurality of bolt clearance grooves 21 on the outer periphery of the stator core 17A. The grooves 21 are linearly formed to continue from the top to bottom in parallel relative to the laminating direction of the thin metal sheets 17a. These bolt clearance grooves 21 are, for example, provided at intervals of 10xc2x0 relative to a circular center of the stator core 17A.
As described above, the circular cylinder body is formed by spirally laminating the long, thin metal sheets 17a. In addition to this example, it is also possible to assemble another stator core with a predetermined thickness by laminating a plurality of thin metal sheets (of thin plate ring shape) to form a circular cylinder body and then making several welds on the outer periphery in the same manner as above.
According to the conventional stator core 17A as described above, welds are linearly made to continue from the top to bottom on the circular cylinder body and in parallel in the laminating direction of the thin metal sheets (i.e. in parallel along the bolt clearance grooves 21). In this case, if an attraction force between the rotor 6 and the stator 7A is applied to the stator core 17A, there has been a problem whereby the linearly made welding location becomes a node and as shown in FIG. 20, the whole stator 7A causes the mode of oscillation in a diametric direction.
Also, as shown in FIG. 21, in a stator core 30 which is disclosed in Japanese Laid-Open Utility Model Publication (Kokai) No. Sho 53-141410, there is shown that a non-welding portion 31 is partially provided. Here are formed welds 32 that are continuous vertically at several welding locations on the outer periphery of a stator core 30 with a predetermined thickness S. However, in this case, since there are many welds 32 that are continuous vertically at each welding location, the welds 32 are not always made dispersely in the peripheral and vertical directions of the outer periphery of the stator core. Therefore, the welds 32 become the node and they do not serve to eliminate the role. Since there are various orders in the vehicle AC generator where the engine speed covers a wide range, there is still a problem that the welds come to serve as one of the nodes and still generate the mode of oscillation.
It is therefore an object of the present invention to solve the above-mentioned problems and to provide an improved stator core and a method for its production that make it hard to produce an oscillation node in a diametric direction and can decrease the mode of oscillation.
According to the present invention, there is provided a stator core of an AC generator comprising a plurality of first cylinder bodies each having a predetermined thickness of 1/N (where N is a natural number greater than 2), of a predetermined axial thickness of the stator core, wherein each first cylinder body is formed by laminating a plurality of thin metal sheets. A second circular cylinder body is formed by laminating the plurality of first cylinder bodies to have the axial predetermined thickness, wherein the pluralities of first cylinder bodies contribute as a plurality of core units in the second cylinder body, and wherein each of the plurality of thin metal sheets is fixedly secured by welding.
Further, the core units can be fixedly secured by welding on the outer or inner periphery of the second circular cylinder, and a peripheral welding location between two adjacent first cylinder bodies can be selected to be different from a welding location of the thin metal sheets of each of the first cylinder bodies. In addition, the welding locations of the thin metal sheets of the first cylinder bodies can be arranged to be discontinuous in the laminating direction of the thin metal sheets in at least one of the core units.
The stator core is produced by the steps of laminating the thin metal sheet to form in advance a plurality of core units of a circular cylinder shape with the thickness of 1/N (N is a natural number of more than 2) of a predetermined thickness in the laminating direction, laminating this plurality of core units to form a circular cylinder body with a predetermined thickness; and securing the core units to one another.
The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings.